In the prior art U.S. Pat. No. 7,300,230 B2 requires the excavation of a hole to access the pile cap or ground beams and using transfer beams to attach the pile head. However this would be undesirable in the case of a raft foundation, as this excavation will weakened the slab. Moreover, in most cases the slab will be strong enough to support the underpinning pile if it can be placed underneath the slab. Hence, a pin hole pre-bored in the slab will ensure that the shear in the concrete slab is not compromised, especially if the underpinning pile is placed near to the main support columns.
In the prior art U.S. Pat. No. 2006/0216117 A1, teaches the insertion of a bracket through an opening and far enough into the excavated area underneath the slab. The soil below the enlarged opening is excavated to allow room for the subject bracket to be inserted below the slab. The bracket is then welded with rebar and concrete is introduced into the excavated region and hardened around the bracket and rebar to produce a three dimensional plug so that it can support the slab. Clearly, until the concrete hardens in this prior art, the full structural capacity of the slab around the opening will be compromised during lifting. Whereas the present invention overcomes this difficulty and allows the slab to be immediately lifted up or used to drive the underpinning pile without using concrete, rebars or likes to form a plug. In this same prior art, the lifting mechanism is through tightening the screws in the pair of threaded rods, which is independently attached to the tubing which is not connected directly to the brackets. Thus any failure in the weakest link can occur between tubing and the treaded rods or between the tubing and the bracket. The present invention has large welding contact areas and a plurality of welded wedges to support the pile head directly on to the slab, thus avoiding a double weak link as in faced in the prior art.